We had the same discussion on that matter. If you remove the outer Border of RadDateTimePicker
in ReadOnly state it's strange, indeed.
We finally decided to keep the behavior, which is by design.
Any attempt to revert back these changes could lead to a potential breaking change, that we want to avoid.
Currently, if you need this Border, I may suggest you to modify the template of TextBox against Office2013
and remove the animation that resets the BorderThickness
of the root container.
Hope this helps.
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